Pipes containing fluid under pressure are prone to leak from a number of causes, including corrosion, freezing, deterioration of fixtures, etc. This is of particular concern in a household residence where protracted leakage of plumbing pipes can cause much property damage to the structure and contents. A number of systems have been devised to automatically shut off water in a plumbing system in the event of a leak. One example is found in U.S. Pat. No. 5,038,820 to Phillip Ames, et al. This system uses a "pivotal flapper" positioned within a pipe, which flapper is pivoted upward due to water flow in the pipe. The flapper then operates a switch which starts a timer which, in turn, operates a motor to control a valve after the expiration of a preset time period. Another example is found in U.S. Pat. No. 4,589,435 to Aldrich, which is very similar in that it uses a probe positioned within a pipe and which is moved by fluid flow to trigger a timing circuit. The timer, in turn, controls a solenoid which closes off a valve to shut down fluid flow after a preset time period. Neither the Ames or the Aldrich patent allows their systems to be set to be triggered at different flow rates. This is a problem, for example, where it is desirable to allow a certain minimal flow volume for humidifiers, ice makers, etc., but to shut off in response to a larger flow volume. In addition, both Ames or Aldrich are relatively complex systems which makes them expensive.
It is clear, then, that an improved automatic shut-off device for closing plumbing or other fluid carrying pipes is needed. Such a device should preferably be simple and inexpensive, but be capable of adjustment to allow for different flow thresholds upon installation.